Many and varied compositions, products, appliances, depositors, applicators, dispensers, injectors and devices are well known in the art in which the timing or spacing of administration or absorption of an active agent is regulated by the structure or physical arrangement of elements so that a single administration provides a gradual but continuous or sustained feeding of the active agent to a system by slow or differential release. All of such prior art devices and the like, however, are characterized by at least one feature which adversely affects control over their rate of sustained or differential release or which detracts from the practical benefits attendant the long-term continuous administration of various active agents both to humans, animals, and into other environments.
An osmotic dispenser too has been proposed which is capable of delivering drug solution at a relatively constant rate. See Rose and Nelson, Austral. J. Exp. Biol., 33 pp. 415 - 420 (1955). The Rose et al injector consists of three compartments and a clamp to hold a semi-permeable membrane. The motive force of the injector depends on the osmotic pressure developed by a saturated aqueous solution of Congo red against water. This solution is contained in a partially collapsed rubber compartment and is separated from a second water compartment by the semi-permeable cellophane membrane. The partially collapsed bag is placed in a glass ampoule, with the drug compartment of the device being defined by the space between the Congo red bag and the glass ampoule. The ampoule is also provided with drug release means and when the drug compartment is charged with a drug solution by osmosis water will move into the Congo red solution thus expanding the rubber compartment and providing the mechanical force to eject the drug out of the apparatus.
The Rose et al device, however, has substantial inherent disadvantages which has prevented its wide acceptance by the medical community. In the first place, the use of a solution as the drug vehicle (1) will not permit high concentration of drug to be embodied within the device; (2) such solutions exhibit the deleterious tendency to be released from the device by simple leaching; and (3) many chemical substances on prolonged storage in a dissolved state undergo chemical deterioration. The reference injector is moreover cumbersome in that it depends for its motive force on a separate water compartment rather than its environment. In addition, the Rose et al device is essentially only a research or experimentation tool, is complex in construction and is at least literally restricted to a Congo red solution to produce the osmotic driving force and to a cellophane osmotic membrane. See also Rose and Nelson, Austral. J. Exp. Biol., 33 pp. 411 - 414 (1955).